Master cylinder for hydraulic brakes



March 28, 1939. c H. KINDL 2,152,485

MASTER CYLINDER FOR HYDRAULIC BRAKES Filed Oct. 29, 1954 Gum 1 116 Patented Mar. 28, 1939 v I 2,152,485

' UNITED STATES PATENT OFFICE.

MASTER CYLINDER FOR HYDRAULIC BRAKES Carl B. Kindl, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mlcln, a corporation of Delaware Application October 29, 1934, Serial No. 150.526 1 Claim. (01. sip-54.6)

This invention relates to fluid transmitting seated in a groove in the end of the cylinder. mechanism such as is used for applying vehicle This ring serves to prevent the escape from the brakes and doing other. useful work. It is incylinder of the head I9. A dust protecting boot tended more particularly as an improvement in 53 is secured to the end of the cylinder by 5 the master cylinder of a hydraulic brake system fastening means 55 and to the rod l5 in any 5 for vehicles. convenient manner. The cylinder is formed with The object of the invention is to improve the lugs 56 adapted to engage a vehicle part 51 to operation ofthe hydraulic medium in applying which it is secured by fastening means 59. The the brakes. end of conduit 9 adjacent the assembly II is 10 A further object consists in providing an ims cured to a fit i 6| t r aded i e end of 10 proved master cylinder and reservoir assembly the Cylinder whereby the action of the hydraulic medium is Formed integrally With the cylinder is a improved. ervoir 63. The reservoir has an opening at 65 Other objects and advantages will be underv d y a f ld d aph a m 6 wh h stood from the following description. p m s clamped under a cover 69 having an 15 In the drawing: air vent II and secured by fastening means 13.

Fig. 1 is a diagrammatic view showing the re- The drawing a h ws a plu 5 ov rin an lationof the master .cylinder and reservoir as- Opening The Wall 19 between Cylinder sembly. v and reservoir 63 is provided with a suitable com- 2 Fig.2 is a view in vertical section through the sa e p n 8 T s p n is u ov- 2o master cylinder and reservoir. ered by the piston when in its retracted position Referring to the drawing, numeral 5 repres shown in Fig. 2. The separating wall is also sents the wheels of a vehicle, each wheel having formed With an apertured bOSS 33 from which a a drum 1 housing suitable expanding brake shoes, Passage 35 leads t0 the e 0 45 b we the not shown. These sh e are expanded by com piston and the wall 31. A cap 81 is threaded into 2., ventional hydraulic wheel cylinders, these not the It is apertured as at Within the being illustrated. The cylinders are operated by cap is a Valve Positioned as to close the a fluid medium transmitted through conduits 9 opening 89 by a Sp The Valve 9| is p which are connected to a master cylinder and Vided with a Small Compensating ap u e 30 reservoir assembly indi t d as a whole by The operation of the system provided with this 1:0

.meral ll. A- pedal [3 normally held in relea ed novel assembly is as follows; position by a spring I4 is used to push a rod 5 Fig. 2 represents the parts in the position they having a ball end I! k t t enlarged occupy when the brakes are released, any tenhead IS on one end of a piston rod 2 o the dency to unequal pressure conditions between the a disc 25 bearing against which i a cup-shaped pensated by the apertures 8| and 95. When the packing 21 held against the disc by a spri 29 pedal is depressed, the piston moves to the right The spring engages ab t nt-, 3 one abutment and at once covers opening 8|. The hydraulic lying against the packing 21 and the other seated medium is forced out through the conduit 9 to the 40 in a groove and engaging a shoulder 33 at t several wheel cylinders where it acts upon the 40 end of the rod 2|. Th piston reciprocates in a pistons of the wheel cylinders to expand the cylinder 35, being uid d for rectilinear moveshoes into contact with the wheel drums. In so ment by the head I9 as it slides in the outer end moving, from Chamber which c amber s of the cylinder. being reduced in capacity, may escape through The cylinder is divided by l 31 engaging slots 49. The sealing wall 4| functions to prevent 45 a shoulder 39. Together with w ll 31 i a Sea}- any transference of fluids between chambers 43 ing closure member 4| apertured for the passage and 45. To prevent the development of suction of rod 2| and so fittin th d d cylinder in chamber 45 as the piston 25 moves forwardly, wall as to prevent the passage of air or liquid Valve 9| Opens and the y u c med um om between the regions 43 and 45 on opposit Sides the reservoir 63 enters the chamber 45 and keeps of the wall. A spring ring 41 is snapped into a fiileli- Subsequent 0 brake pp Pre groove of the cylinder to hold the parts 31 d sure on the pedal is relieved and spring l4 restores 4! in position. The head It! may be pr vid d it and the piston to its brake release position. In with grooves 49 to permit the free passage of doing so it may move the piston too rapidly for air to and from chamber 43. A ring 5| is shown the fluid from the brake cylinders to keep the 55 other end of rod. 2| is ashoulder 23 engaged by cylinder chambers and the reservoir being comvice the space 45 has been filled with fluid from the reservoir in the forward stroke of the piston and that this space is being reduced in capacity by the retracting movement of the piston. There will therefore be a fluid fiow from this space 45 around the piston to chamber 35 to break the vacuum because the only other escape-oflers considerable resistance and is unable to permit the ready escape of the trapped fiuid.

The device may be used as a pump in the event that there is a lack of hydraulic medium in the system. Suppose, for example, the pedal reaches the floor before the brake shoes engage the drum owing to a lack of hydraulic medium. The foot may be lifted from the pedal. Its spring M will then reversely rotate the pedal, thereby pulling back the piston. It may be then pushed forward again by the foot to apply the brakes, the pedal no longer reaching the floor. In the retracting movement of the piston some of the hydraulic medium reenters chamber 35 from the conduit; some passes the piston cup 21 from chamber 45 to-chamber 35; and a little is restored to the reservoir through aperture 35. The space 35 is thus replenished from chamber 45 as well as from the conduit 3 and the wheel cylinders because the backward fiow of the medium through the conduit 3 toward chamber 35 influenced by the brake releasing springs is supplemented by the tendency to build up pressure in chamber 45 and deliver the hydraulic medium from chamber 45 to chamber 35. The subsequent pressure on the piston then operatu against a greater quantity of the medium in the system and the brakes are applied before the pedal reaches the floor. When the brakes are to be released the piston moves to the left and the chamber 35 is again filled, the filling beingaccomplished in part by thepassage of the 'mediumaround the piston from chamber 45 as before. when the piston is fully retracted as in Fig. 2,.the shoe releasing springs force back the excess medium to the master cylinder and out through compensating opening 3| to the reservoir. It will be seen that the head I! guides the piston for rectilinear motion but that the chamber 43 is always subject to atmospheric pressure only and has no function in connection with the operation of the t mon of the medium as does chamber 45.

It is a matter of importance that the flow of the medium should be partly from chamber 45 to chamber 35 when the piston is being retracted whether for the purpose of pumping up the system or for releasing the brakes for the reason that otherwise the tendencyto create suction in chamber 35 might cause air to leak into th system at the wheel cylinders, which air woul obviously interfere with the action of brake ap tion. Some known constructions have attem ted to overcome this difliculty by providing retarding means in the conduit to check the return flow of the hydraulic medium. Any such retarding means. obviously adds to the resistance to be overcome when applying the'brakes. I find that it is better to use the construction comprising the sealed wall 4| together with the valve 9|, which constructions cooperate. to tend to exert positive pressure to supply the chamber 35 from chamber 45 as the piston moves toward the rear. In this way no suction is developed in chamber 35 such as might'cause an inflow of air at the wheel cylinders of the system. To whatever extent the retracting movement of the piston exceeds the return movement of the hydraulic medium, to that extent the medium is supplied to region 35 by a -flow around the piston. -'lI'he pressure in chamber 45 caused by the spring l4, additional to that required to prevent the development of suction in chamber 35, causes a gradual discharge of the hydraulic medium through aperture 95. This has the added function of checking a too rapid return of the pedal to its released position.

I claim:

In a hydraulic brake system, a master cylinder, a piston slidable within said cylinder, a head reciprocable in one end of said cylinder, a rod connecting said head and piston, sealing means secured in said cylinder between said head and piston, said rod slidable through said sealing means, said cylinder having a discharge outlet at its other end, a reservoir integral with said cylinder, a restricted opening between said reservoir and cylinder at that part of the latter corresponding with the retractedposition of the piston, said cylinder having a boss integral therewith and projecting into the reservoir, a valve controlled passage in said boss affording communication between the reservoir and that part of the cylinder between the piston and-the sealing means, and means engaging said head to reciprocate said head and piston. I

CARL H. KINDL. 

